.\"	$OpenBSD: rdate.8,v 1.37 2015/02/10 13:10:27 deraadt Exp $
.\"	$NetBSD: rdate.8,v 1.4 1996/04/08 20:55:17 jtc Exp $
.\"
.\" Copyright (c) 1994 Christos Zoulas
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by Christos Zoulas.
.\" 4. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: February 10 2015 $
.Dt RDATE 8
.Os
.Sh NAME
.Nm rdate
.Nd set the system's date from a remote host
.Sh SYNOPSIS
.Nm rdate
.Op Fl 46acnopsv
.Ar host
.Sh DESCRIPTION
.Nm
displays and sets the local date and time from the
host name or address given as the argument.
The time source may be an RFC 5905 protocol SNTP/NTP server
or an RFC 868 TCP protocol server,
which is usually implemented as a built-in service of
.Xr inetd 8 .
By default,
.Nm
uses the RFC 5905 SNTP/NTP protocol.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl 4
Forces
.Nm
to use IPv4 addresses only.
.It Fl 6
Forces
.Nm
to use IPv6 addresses only.
.It Fl a
Use the
.Xr adjtime 2
call to gradually skew the local time to the
remote time rather than just hopping.
.It Fl c
Correct leap seconds.
This should be used only when synchronizing to a server
which does not correctly account for leap seconds.
.It Fl n
Use SNTP (RFC 5905) instead of the RFC 868 time protocol.
This is the default.
This protocol counts 32 bits of seconds from January 1, 1900
and will rollover in March 2036.
.It Fl o
Use an RFC 868 TCP protocol server instead of SNTP.
This protocol is obsolete as it is not capable of representing
dates past January 19, 2038 03:14:07 GMT.
.It Fl p
Do not set, just print the remote time.
.It Fl s
Do not print the time.
.It Fl v
Verbose output.
Always show the adjustment.
.El
.Sh FILES
.Bl -tag -width /var/log/wtmp -compact
.It Pa /var/log/wtmp
record of date resets and time changes
.El
.Sh EXAMPLES
To get the legal time in Germany, set the
.Pa /etc/localtime
symlink to
.Pa /usr/share/zoneinfo/right/Europe/Berlin
and issue the following command:
.Pp
.D1 Li "# rdate -v ptbtime1.ptb.de"
.Pp
The command of course assumes you have a working internet connection
and DNS set up to connect to the server at
.Sy Physikalisch-Technische Bundesanstalt
in Braunschweig, Germany.
.Sh SEE ALSO
.Xr date 1 ,
.Xr adjtime 2 ,
.Xr inetd 8 ,
.Xr ntpd 8
